While the Nyrian's were taking over USS Voyager, and Chakotay and Larson were the two remaining crew members, Chakotay checked a systems analysis panel in the corridor that listed among other things the status of the photosynthetic bioprocessor. (VOY: "Displaced")

Not mentioned in dialogue, the photosynthetic bioprocessor could only be read on the panel - which was part of the corridor standing set over the seven years of Star Trek: Voyager. The function, or details of the photosynthetic bioprocessor were never discussed.